Area code 510 is a California telephone area code serving most of the East Bay. It split off from area code 415 on September 2, 1991. It covers most of Alameda County (including the city of Oakland but excluding Dublin, Livermore, Pleasanton, and Sunol), and western Contra Costa County.
In the United States, AT&T originally used area 510 for its TWX (TeletypeWriter eXchange) network. Western Union acquired the TWX network in 1969 and renamed it Telex II. By the 1970s, three TWXs had been added (710 in the Northeast, 810 in Michigan, Ohio, Indiana, Kentucky, North Carolina, South Carolina, Georgia, Florida, Louisiana, Mississippi, and Alabama; and 910 west of the Mississippi). Each major city had one or more local exchange prefixes. Western Union upgraded the network to "4-row" ASCII operation (it previously used both "3-row" Baudot and ASCII transmission) and decommissioned the special TWX area codes in 1981.
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Meetings were held in Berkeley, Oakland and Hayward in January and February 2017 to discuss area code relief for 510, which is forecast to run out of numbers by mid-2018. The relief method will be an overlay and is expected to go into effect in December 2017. As of May 2017, the overlay area code had not officially been assigned; however, the 341 area code was assigned to provide relief to the region in 1997 (in conjunction with the 925 area code split) until number rationing procedures eliminated the need for the overlay at that time. It is unclear if 341 has still been set aside for this purpose; however, the area code remains unassigned as of November 2017.
|California area codes: 209, 213/323, 310/424, 408/669, 415/628, 442/760, 510, 530, 559, 562, 619, 626, 650, 657/714, 661, 707, 747/818, 805, 831, 858, 909, 916, 925, 949, 951|
|West: 415, 650||area code 510||East: 925|